Large sawmills typically cut logs into lumber in stages. In the first stage, or primary breakdown, the logs are rotated to a desired angle and conveyed through chippers and/or saws that cut the logs into cants. Some mills cut flitches from the cants by cutting the cants longitudinally along planes generally parallel to the machined faces. Other mills profile side boards along the machined faces of the cants, and the cants are then cut longitudinally to release the side boards. In both cases, the log is cut into a center cant and one or more additional pieces (or chipped into a center cant and chips) during this stage.
In the second stage, or secondary breakdown, the center cant is cut into center boards by a gang saw, any flitches are cut into outer boards by an edger, and all of the boards are trimmed to desired lengths.
In many sawmills, some or all of the machine centers are controlled automatically by a control system based on workpiece position, orientation, dimensions, and other information obtained by scanners. The workpiece is conveyed through a scan zone upstream of the machine center, and the computer system uses the profile data to position and/or cut the workpiece into the desired pieces.